In research and development, and in the quality control, of fibrous slurries used for forming articles by drawing the liquid through a permeable member, having passages sufficiently small to prevent the solids in the slurry from passing therethrough, it is often desirable to determine the filtration, or drainage, characteristics of the slurry using only a relatively small slurry sample. By making an accurate determination on a small sample, undesirable slurry ingredients and/or slurry compositions can be detected and eliminated. Also, by testing slurries intended for use on a production unit, data is obtained that can be used to pre-set process parameters for each different slurry to reduce the amount of defective products produced. However, to accomplish these objectives it is essential that the results produced by the test accurately represent the results that the production unit will produce. The type of production units referred to here are disclosed in detail in numerous U.S. Pat. Nos., e.g. 2,182,353, 2,246,537, 2,322,592, 3,095,346 and 3,715,230.
The tests previously used to determine the drainage characteristics of slurries comprising asbestos fibers and hydraulic cement particles have failed to produce results that accurately represent the performance of the slurries in a production sized process or are too complex and require too much time to be practically useful. Several tests have been proposed and used, but each suffers one or more of the defects just described.
One test frequently used, a standard test used in the paper industry, is called the TAPPI test. In this test, a fixed volume of slurry is poured into a graduated transparent cylinder having a 60 mesh (U.S. STD.) screen located in its bottom. The time required for a fixed volume of the liquid carrier to pass through the screen, under the influence of gravity and the slurry head in the cylinder, is measured to determine the drainage characteristics of the slurry. The results obtained using this test on slurries containing asbestos fiber are frequently not representative of the results found when the slurries are used in production sized wet process equipment for making asbestos/cement sheets, pipe, etc.
Another test, called the Alpharater test, is similar to the TAPPI test, except a partial vacuum of 200 mm of mercury is established on the down stream side of the 60 mesh screen. Like the TAPPI test, this test produces results that are not representative of those obtained on production sized wet machines.
A third test that has been used is called a Fiberator test. This test is similar to the Alpharater test, except that the screen area used is larger and the slurry head above the screen is smaller. In addition to measuring the filtrate volume, the weight of the layer of solids built up on the 60 mesh screen, in a fixed period of time, is also determined. While this test produces results that more closely approximate the results obtained on production sized equipment, this test is complicated and requires more time than desired.
The object of the present invention is to provide a test, and accompanying apparatus, that is simple, fast, and that produces results that will be representative of production sized equipment.